1. Field of the Invention
This invention relates to a gas filter element useful for removing fine particles of foreign matter in gaseous fluids.
2. Description of the Prior Art
In this connection, there has been known in the art a liquid filter element as disclosed in U.S. Pat. No. 4,501,663, which is composed of a plural number of thin disk-like units each having filter membranes fixedly bonded on both sides thereof and being connected successively in a spaced relation in the axial direction, forming liquid induction channels between the opposing filter membranes of adjacent units.
The filter element of this sort, in which the liquid flowing into the channels between the adjacent units is passed through the filter membranes of a relatively large area on the opposite sides of each liquid induction channel, has an advantage that the element can afford a relatively large filtration area compared with its entire volume. However, in order to secure sufficient strength of the filter membranes, it has been the general practice to fixedly bond the membranes not only to the mount portions at the inner and outer peripheral edges of the holder but also to a large number of ribs which are provided in closely spaced relation between the inner and outer mount portion of the holder. The total area taken up for bondage between a filter membrane and a holder usually amount to an unignorably large proportion of the area of the filtration membrane as a whole, resulting in a material reduction in the effective filtration area of the membrane. Presumably, such a reduction is as large as 15% or more in most cases.
Further, in a case where part of the holder is dissolved by the use of a solvent or where an adhesive is applied to a large number of ribs, it is required to bond the filter membranes to the holder very carefully since application of an excessive amount of solvent or adhesive might block the pores in the membranes. There is also a problem that, unless the bonded portions are dried to a sufficient degree, it is difficult to obtain a clean filtrate fluid since the solvent would be entrained into the filtrate while passing through the filter element.
In order to eliminate these problems, it is desirable to fix the membranes to a holder by thermal fusion bonding, which is however extremely difficult to apply to the bondage between a membrane and a large number of closely spaced ribs in view of the problem of partial meltdown which might occur to the filter membranes.